Aegina, which the Athenians had attacked and…

The central Greek line of Athenian expansion is bound to bring a collision with Sparta, which enters the war in 458 in response to …

…an appeal by its “mother country” Doris, from which the primeval Dorians are believed to have set out to undertake the invasion of the Peloponnese.

This tiny state in central Greece is currently having trouble with its neighbor Phocis.

The religious and sentimental factor in Sparta's response is not negligible, but Sparta may have other aims as well: Boeotia may be a target. (There is evidence of this in Diodorus Siculus, a Greek historian of the first century BCE, though not in Thucydides.)

The Greek task force had achieved initial successes, but they have been unable to capture the Persian garrison in Memphis despite a three-year long siege.

A strong internal federation, along with Athenian aid, enables the Phocians to regain control of the oracle at Delphi in 457 at the beginning of the “Second Sacred War” against Phocis.

Sparta, probably distracted (or left weakened) by the great helot revolt, is largely inactive in the conflict; …

…on the Spartans' return from Doris in 457 BCE, however, the land armies of Sparta and Athens meet at Tanagra in Boeotia.

Cimon presents himself to the Athenian generals and begs leave to fight in the ranks but is refused.

He adjures his personal followers, suspected like him of favoring the Spartans, to fight bravely, and they all perish in the large-scale but indecisive battle; …

…perhaps this event causes a revulsion of bitter feeling against Cimon.

In any case, Pericles himself, who has succeeded the assassinated Ephialtes as head of the democratic party, proposes and obtains an abbreviation of Cimon's exile.

On his return, he works for peace with Sparta, and is said to have been allowed to resume the war with Persia, much preferred to fighting other Greeks.

Athens makes an alliance (almost certainly in 457 BCE) with Segesta, an inland half-Greek Sicilian city; ...

…elsewhere in Sicily, Naxos stands in opposition to Syracuse after 461 BCE.

Ducetius, a Hellenized leader of the Siculi, seizes his opportunity to weld the native communities of east Sicily into a powerful federation during the confusion that follows the collapse of tyranny in Syracuse and other Sicilian states in 460 BCE.

Enjoying the goodwill of the Syracusan democracy, he enlists its help in driving out the colonists of the former tyrant Hiero from Catana and restoring it to its original Chalcidian inhabitants.